ACS-WFC-DITHER-BOX
pointing patterns
This is a two-dimensional 4-point dither pattern,
with the following allowable parameter ranges:
Pattern_Number: 1
Pattern_Type: ACS-WFC-DITHER-BOX
Pattern_Purpose: DITHER
Number_Of_Points: 4
Point_Spacing: 0.01 - 10.0 (arcseconds)
Line_Spacing: 0.01 - 10.0 (arcseconds)
Coordinate_Frame: POS-TARG
Pattern_Orient: 0.0 - 360.0 (degrees)
Angle_Between_Sides: 0.0 - 360.0 (degrees)
Center_Pattern: ? (YES or NO)
The following versions of this Pattern_Type are projected
onto the detector pixel space in the graphic above.
The
default pattern has relative pixel coordinates
(0, 0), (5.0, 1.5), (2.5, 4.5), (-2.5, 3.0).
It is a parallelogram pattern designed for optimal half-pixel sampling
in both x and y, with overall dimensions large enough to help
reject the larger detector artifacts.
Pattern_Number: 16
Pattern_Type: ACS-WFC-DITHER-BOX
Pattern_Purpose: DITHER
Number_Of_Points: 4
Point_Spacing: 0.264
Line_Spacing: 0.185
Coordinate_Frame: POS-TARG
Pattern_Orient: 20.86
Angle_Between_Sides: 69.07
Center_Pattern: NO
POS TARG equivalent: 0.000, 0.000
0.247, 0.094
0.124, 0.232
-0.124, 0.138
This
diagram
shows how much this pattern's shape varies
across the entire WFC field-of-view, as a result of
scale variation.
The following pattern was designed for the
UDF observations. It
is slightly more compact than the default pattern above,
and therefore reduces the effect of the
scale variation on the integrity of the pattern across the
entire WFC field-of-view:
Pattern_Number:
Pattern_Type: ACS-WFC-DITHER-BOX
Pattern_Purpose: DITHER
Number_Of_Points: 4
Point_Spacing: 0.171
Line_Spacing: 0.171
Coordinate_Frame: POS-TARG
Pattern_Orient: 30.16
Angle_Between_Sides: 145.82
Center_Pattern: NO
POS TARG equivalent: 0.000, 0.000
0.148, 0.086
0.222, 0.240
0.074, 0.154
The
compact pattern
is about as compact as possible, therefore it
minimizes the effect of the scale variation on the
integrity of the pattern across the entire WFC field-of-view,
at the expense of not rejecting some of the
larger detector artifacts.
Pattern_Number:
Pattern_Type: ACS-WFC-DITHER-BOX
Pattern_Purpose: DITHER
Number_Of_Points: 4
Point_Spacing: 0.104
Line_Spacing: 0.053
Coordinate_Frame: POS-TARG
Pattern_Orient: 18.31
Angle_Between_Sides: 80.79
Center_Pattern: NO
POS TARG equivalent: 0.000, 0.000
0.099, 0.033
0.074, 0.080
-0.025, 0.047
This
expanded pattern
is designed to move an object completely off of it's own PSF between
exposures. It is similar to the other BOX patterns here,
but has overall dimensions about 4 times larger. This is
optimized for smallish objects near the defined aperture,
i.e. when the shape of the pattern near the
edges of the field-of-view is less important.
Pattern_Number:
Pattern_Type: ACS-WFC-DITHER-BOX
Pattern_Purpose: DITHER
Number_Of_Points: 4
Point_Spacing: 0.841
Line_Spacing: 0.795
Coordinate_Frame: POS-TARG
Pattern_Orient: 19.91
Angle_Between_Sides: 97.36
Center_Pattern: NO
POS TARG equivalent: 0.000, 0.000
0.790, 0.286
0.618, 1.063
-0.173, 0.776
This pattern is not plotted above, but it's relative dimensions
can be viewed in this
comparison plot.
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